A high-speed solenoid valve is used to open and close a fluid passage for various types of control in a hydraulic circuit, for example. Such a high-speed solenoid valve has superior characteristics; that is, it can be switched over at high frequency, can be operated by directly receiving a digital signal from a control unit such as a microcomputer, and also can perform flow rate control through switching at high frequency. An example in which the high-speed solenoid valve is employed for drive control of a hydraulic cylinder will be described below with reference to the drawing.
FIG. 1 is a circuit diagram of a hydraulic circuit using a high-speed solenoid valve. In the drawing, denoted by reference numeral 1 is a hydraulic pump and 2 is servo cylinder. Connected to a rod of the servo cylinder 2 is a displacement volume varying mechanism, e.g., a swash plate, of a variable displacement hydraulic pump (not shown). Reference numeral 3 designates a reservoir (tank), 4A is a high-speed solenoid valve interposed between the hydraulic pump 1 and the head side of the servo cylinder 2, and 4B is a high-speed solenoid valve interposed between the head side of the servo cylinder 2 and the reservoir 3.
In order to properly control a delivery rate of the variable displacement hydraulic pump, when a control signal is outputted from the microcomputer (not shown) to the high-speed solenoid valve 4A, for example, the high-speed solenoid valve 4A is switched to the lower shift position in the drawing. As a result, the servo cylinder 2 is driven in the direction of extension of the rod dependent on a difference in the pressure receiving area between both chambers of the servo cylinder 2, thereby increasing (or decreasing) a tilting amount of the swash plate. On the contrary, when a control signal is outputted to the high-speed solenoid valve 4B to switch it over to the lower shift position, the head side of the servo cylinder 2 is communicated with the reservoir 3, whereby the rod is contracted to decrease (or increase) a tilting amount of the swash plate. That operation is carried out with high responsibility by direct application of a digital signal to the valve from the microcomputer.
While the high-speed solenoid valve has the superior characteristics as mentioned above, it also has the problem below. More specifically, to achieve a high-speed operation, the high-speed solenoid valve must be so structured as to have a small diameter and short stroke of a spool. Therefore, the pressure loss is increased and the flow rate that can be handled is decreased. This necessarily limits the size, output and other rated values of the hydraulic cylinder, which can be directly controlled thereby. One means for solving this problem is to raise a pressure supplied to the high-speed solenoid valve. But, this means is unfavorable in that the energy loss becomes too large. Another solution means, of increasing the size of the high-speed solenoid valve, is difficult to practice from the above structural reason, so long as the current operating voltage is employed as it is. If the valve size is increased without respect of such limitations, the primary characteristic of the high-speed solenoid valve, i.e., the responsivity, would be deteriorated.
In view of the above existing state of the art, the inventor has previously proposed a high-speed solenoid valve apparatus disclosed in JP, A, 62-292982. This high-speed solenoid valve apparatus is shown in FIG. 2. Referring to FIG. 2, denoted by 10 is a body which forms an outer shell of the high-speed solenoid valve apparatus and which also has an inlet port 11 and an outlet port 12. Between the inlet port 11 and the outlet port 12, a high-speed solenoid valve section 10A and a logic valve section 10B are juxtaposed in the vertical direction. The high-speed solenoid valve section 10A comprises a first sleeve 13 forming an outer shell thereof, an inlet port 14 formed in the first sleeve 13, a passage 15 selectively communicating with the inlet port 14, an outlet port 16 communicating with the passage 15, and further a spool 17 movably disposed in the first sleeve 13 to open and close the communication between the inlet port 14 and the passage 15, and therefore, the outlet port 16. The logic valve section 10B comprises a second sleeve 18 disposed in the body 10 to surround the first sleeve 13 of the high-speed solenoid valve section 10A, an inlet port 19 formed in the second sleeve 18, an outlet port 20 selectively communicating with the inlet port 19, and a poppet 21 for opening and closing the communication between the inlet port 19 and the outlet port 20. The poppet 21 has a control chamber 22 formed therein, and a small-diameter penetration (through) hole 23 communicating between the inlet port 19 and the control chamber 22.
Denoted by 24 is a return spring disposed in the control chamber 22 of the poppet 21 for applying a restoring force to the poppet 21 and the spool 17, and 25 is a stopper disposed between the first sleeve 13 and the second sleeve 18, i.e., between the spool 17 and the poppet 21, for restricting movements of the spool 17 and the poppet 21. The return spring 24 and the stopper 25 are components commonly shared by the high-speed solenoid valve section 10A and the logic valve section 10B. Then, the inlet port 19 of the logic valve section 10B is communicated with the inlet port 11 of the body 10 and also with the control chamber 22 via the small-diameter penetration hole 23 as mentioned above. The control chamber 22 is in turn communicated with the inlet port 14 of the high-speed solenoid valve section 10A via a hole formed through the stopper 25. Further, the outlet port 20 of the logic valve section 10B and the outlet port 16 of the high-speed solenoid valve section 10A are communicated with a passage 26 which is formed in the body 10 and communicating with the outlet port 12 of the body 10.
The above high-speed solenoid valve apparatus operates as follows. When a coil of the high-speed solenoid valve section 10A is not energized, the spool 17 is pushed by the return spring 24 upwards in the drawing so that the inlet port 11 of the body 10, the inlet port 19 of the logic valve section 10B, the small-diameter penetration hole 23, the control chamber 22, and the inlet port 14 of the high-speed solenoid valve 10A are blocked off by engagement of valve seats respectively formed by the first sleeve 13 and the spool 17 with respect to the passage 15 and the outlet port 16 of the high-speed solenoid valve 10A, the passage 26 of the body 10, and the outlet port 12.
In addition, because the pressure in the inlet port 11 of the body 10 and the pressure in the control chamber 22 are equal to each other, the poppet 21 is pushed downwards on the drawing by a pressing force due to a difference in the pressure receiving area between the upper and lower surfaces of the poppet 21 and also a resilient force of the return spring 24, whereby the inlet port 11 of the body 10 and the inlet port 19 of the logic valve section 10B are blocked off with respect to the outlet port 20, the passage 26, and the outlet port 12 of the body 10.
When the coil of the high-speed solenoid valve section 10A is energized under that condition, the spool 17 of the high-speed solenoid valve section 10A is moved downwards in the drawing against the resilient force of the return spring 24, whereupon the hydraulic fluid in the control chamber 22 is quickly discharged from the outlet port 12 of the body 10 via the inlet port 14 of the high-speed solenoid valve section 10A, the passage 15, the outlet port 16 and the passage 26. On the other hand, the hydraulic fluid introduced from the inlet port 11 of the body 10 via the inlet port 19 of the logic valve section 10B is restricted by the small-diameter penetration hole 23 and cannot flow into the control chamber 22 immediately. The pressure in the control chamber 22 is reduced upon the above discharge of the hydraulic fluid from the high-speed solenoid valve section 10A. Therefore, the force tending to push the poppet 21 upwards in the drawing, which is given by the sum of the pressure applied to the lower surface of the poppet 21 facing the inlet port 19 and the pressure applied to the edge surface of the poppet 21 facing the outlet port 20, becomes greater than the force tending to push the poppet 21 downwards in the drawing, which is given by the sum of the pressure in the control chamber 22 and the resilient force of the return spring 24. This causes the poppet 21 to ascend until it strikes against the stopper 25. As a result, the inlet port 19 of the logic valve section 10B is communicated with the outlet port 20 thereof, and the hydraulic fluid incoming through the inlet port 19 of the body now also passes via the inlet port 19 of the logic valve section 10B, the outlet port 20 and the passage 26 and is then discharged through the outlet port 12 of the body 10, after being joined with the hydraulic fluid outgoing through the outlet port 16 of the high-speed solenoid valve section 10A. At this time, although the return spring 24 is compressed upon the upward movement of the poppet 21 and the force tending to push the spool 17 upwards is increased correspondingly, the force produced by the energized coil of the high-speed solenoid valve section 10A and tending to push the spool 17 downwards remains still much greater. Accordingly, the spool 17 will not be pushed upwards.
In the high-speed solenoid valve apparatus thus arranged, since the high-speed solenoid valve section 10A is associated with the logic valve section 10B, the hydraulic fluid can be discharged through both the outlet port 16 of the high-speed solenoid valve section 10A and the outlet port 20 of the logic valve section 10B, and then through the outlet port 12 of the body 10 after being joined in the passage 26, while the coil of the high-speed solenoid valve section 10A is being energized. It is therefore possible to supply the hydraulic fluid to an actuator or the like operated by the above high-speed solenoid valve apparatus at a flow rate higher than can be supplied in the case of using a conventional high-speed solenoid valve apparatus.
The proposed high-speed solenoid valve apparatus can also reduce the entire dimension of the body 10, i.e., the size of the outer configuration, because of such arrangements that the high-speed solenoid valve section 10A and the logic valve section 10B are vertically juxtaposed in the single body 10, the return spring 24 and the stopper 25 are commonly shared by both the high-speed solenoid valve section 10A and the logic valve section 10B, and the space between the control chamber 22 of the poppet 21 and the valve seat of the spool 17 is set small to be just sufficient to accommodate the stopper 25.
Further, since the space between the control chamber 22 of the poppet 21 and the valve seat of the spool 17 is set small as mentioned above, a response in rising and falling of the pressure in the control chamber 22 can be improved, which results in the good responsivity of the spool 17 and the superior control accuracy.
In spite of these excellent advantages, it is still desired to further reduce the entire dimension of the existing high-speed solenoid valve apparatus.
An object of the present invention is to provide a high-speed solenoid valve apparatus which can solve the above-described problem in the prior art and can further reduce the entire dimension of the apparatus.